This project studies the effects of surgical stress on the endogenous opioid system. It is well known that surgical stress is associated with responses in cortisol as well as in catecholamines; changes in heart rate and blood pressure are also associated with surgical procedures. We have studied the effects of anesthesia induction, abdominal and limb surgery and post-operative morphine administration on plasma levels of beta-endorphin and opioid activity and their relationship to changes in cortisol and post-operative pain medication requirements.